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message_handler.go
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/
message_handler.go
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package kafkax
import (
"context"
"time"
"github.com/Shopify/sarama"
"github.com/ThreeDotsLabs/watermill"
"github.com/ThreeDotsLabs/watermill/message"
"github.com/pkg/errors"
)
// MessageHandler an message processor that is able to receive a ConsumerMessage
// and perform some task with it. Once consumed, if there is a session, it will the offset
// will be marked as processed.
type MessageHandler interface {
ProcessMessages(
ctx context.Context,
kafkaMessages <-chan *sarama.ConsumerMessage,
sess sarama.ConsumerGroupSession,
messageLogFields watermill.LogFields,
) error
}
type messageHandler struct {
outputChannel chan<- *message.Message
nackResendSleep time.Duration
logger watermill.LoggerAdapter
closing chan struct{}
messageParser messageParser
}
func NewMessageHandler(
outputChannel chan<- *message.Message,
unmarshaler Unmarshaler,
logger watermill.LoggerAdapter,
closing chan struct{},
nackResendSleep time.Duration,
) MessageHandler {
return messageHandler{
outputChannel: outputChannel,
messageParser: messageParser{
unmarshaler: unmarshaler,
},
nackResendSleep: nackResendSleep,
logger: logger,
closing: closing,
}
}
func (h messageHandler) ProcessMessages(
ctx context.Context,
kafkaMessages <-chan *sarama.ConsumerMessage,
sess sarama.ConsumerGroupSession,
logFields watermill.LogFields,
) error {
for {
select {
case kafkaMsg := <-kafkaMessages:
if kafkaMsg == nil {
h.logger.Debug("kafkaMsg is closed, stopping ProcessMessages", logFields)
return nil
}
if err := h.processMessage(ctx, kafkaMsg, sess, logFields); err != nil {
return err
}
case <-h.closing:
h.logger.Debug("Subscriber is closing, ", logFields)
return nil
case <-ctx.Done():
h.logger.Debug("Ctx was cancelled, ", logFields)
return nil
}
}
}
func (h messageHandler) processMessage(
ctx context.Context,
kafkaMsg *sarama.ConsumerMessage,
sess sarama.ConsumerGroupSession,
messageLogFields watermill.LogFields,
) error {
msgHolder, err := h.messageParser.prepareAndProcessMessage(ctx, kafkaMsg, h.logger, messageLogFields, sess)
if err != nil {
return err
}
msg := msgHolder.message
receivedMsgLogFields := msgHolder.logFields
ctx, cancelCtx := context.WithCancel(msg.Context())
msg.SetContext(ctx)
defer cancelCtx()
ResendLoop:
for {
select {
case h.outputChannel <- msg:
h.logger.Trace("Message sent to consumer", receivedMsgLogFields)
case <-h.closing:
h.logger.Trace("Closing, message discarded", receivedMsgLogFields)
return nil
case <-ctx.Done():
h.logger.Trace("Closing, ctx cancelled before message was sent to consumer", receivedMsgLogFields)
return nil
}
select {
case <-msg.Acked():
if sess != nil {
sess.MarkMessage(kafkaMsg, "")
}
h.logger.Trace("Message Acked", receivedMsgLogFields)
break ResendLoop
case <-msg.Nacked():
h.logger.Trace("Message Nacked", receivedMsgLogFields)
// reset acks, etc.
msg = msg.Copy()
msg.SetContext(ctx)
if h.nackResendSleep != NoSleep {
time.Sleep(h.nackResendSleep)
}
continue ResendLoop
case <-h.closing:
h.logger.Trace("Closing, message discarded before ack", receivedMsgLogFields)
return nil
case <-ctx.Done():
h.logger.Trace("Closing, ctx cancelled before ack", receivedMsgLogFields)
return nil
}
}
return nil
}
type messageHolder struct {
kafkaMessage *sarama.ConsumerMessage
message *message.Message
logFields watermill.LogFields
sess sarama.ConsumerGroupSession
}
func (mh messageHolder) Copy() *messageHolder {
msg := mh.message.Copy()
msg.SetContext(addMessageContextFields(msg.Context(), mh.kafkaMessage))
return &messageHolder{
kafkaMessage: mh.kafkaMessage,
message: msg,
logFields: mh.logFields,
sess: mh.sess,
}
}
func addMessageContextFields(ctx context.Context, kafkaMsg *sarama.ConsumerMessage) context.Context {
result := setPartitionToCtx(ctx, kafkaMsg.Partition)
result = setPartitionOffsetToCtx(result, kafkaMsg.Offset)
result = setMessageTimestampToCtx(result, kafkaMsg.Timestamp)
result = setMessageKeyToCtx(result, kafkaMsg.Key)
return result
}
type messageParser struct {
unmarshaler Unmarshaler
}
func (mp messageParser) prepareAndProcessMessage(
ctx context.Context,
kafkaMsg *sarama.ConsumerMessage,
logger watermill.LoggerAdapter,
messageLogFields watermill.LogFields,
sess sarama.ConsumerGroupSession,
) (*messageHolder, error) {
receivedMsgLogFields := messageLogFields.Add(watermill.LogFields{
"kafka_partition_offset": kafkaMsg.Offset,
"kafka_partition": kafkaMsg.Partition,
})
logger.Trace("Received message from Kafka", receivedMsgLogFields)
msg, err := mp.unmarshaler.Unmarshal(kafkaMsg)
if err != nil {
// resend will make no sense, stopping consumerGroupHandler
return nil, errors.Wrap(err, "message unmarshal failed")
}
ctx = addMessageContextFields(ctx, kafkaMsg)
msg.SetContext(ctx)
receivedMsgLogFields = receivedMsgLogFields.Add(watermill.LogFields{
"message_uuid": msg.UUID,
})
return &messageHolder{
kafkaMessage: kafkaMsg,
message: msg,
logFields: receivedMsgLogFields,
sess: sess,
}, nil
}
func waitForMessage(ctx context.Context, logger watermill.LoggerAdapter, holder *messageHolder, cancelctx context.CancelFunc) <-chan bool {
waitChan := make(chan bool, 1)
go func() {
defer close(waitChan)
defer cancelctx()
select {
case <-holder.message.Acked():
logger.Trace("Message was ACKed", holder.logFields)
waitChan <- true
break
case <-holder.message.Nacked():
logger.Trace("Message was NACKed", holder.logFields)
waitChan <- false
break
case <-ctx.Done():
logger.Trace("Context has finished", holder.logFields)
break
}
}()
return waitChan
}